The present invention relates to an actuator and more particularly to a shape memory alloy wire actuator.
Shape memory alloys have been known and utilized for many years with various types of actuator devices. One example of such an actuator device is the hydraulic shape memory alloy actuator described in U.S. Pat. No. 4,945,727 to Whitehead et al. The hydraulic shape memory alloy actuator of Whitehead et al. includes a uniaxial shape memory alloy wire constructed of Nitinol and uses a pair of hydraulic cylinders in fluid communication with one another. Each cylinder contains a hydraulic piston. A first hydraulic piston is moved from a first position to a second position when the shape memory alloy wire, connected at one end of the first hydraulic piston and connected at the other end to a fixed point, changes from a martensitic state to an austenitic state upon heating. The second hydraulic piston responds to the movement of the first hydraulic piston by moving from a rest position to an operating position. Upon cooling the wire to change it from the austenitic state back to the martensitic state, the first piston returns to its original position, with a spring provided to return the second piston to its rest position.
Another example of a shape memory alloy wire actuator is disclosed in U.S. Pat. No. 5,345,963 to Dietiker. The Dietiker patent discloses an electrically controlled modulating pressure regulator with a shape memory alloy actuator. A main valve regulates fluid flow between an inlet and an outlet in response to a control pressure produced by a servo valve which is responsive to an outlet pressure and a force applied by a regulator spring to a diaphragm carrying a servo valve closure element. Deformation of the regulator spring can be varied by an electrical current. The regulator spring is in the form of a wire segment of a shape memory alloy through which the electric current passes to vary its temperature and length.
U.S. Pat. No. 6,049,267 to Barnes et al. teaches an adaptive control module using a shape memory alloy in the form of a shape memory alloy electrical switch or relay. The shape memory alloy electrical module includes a strand of shape memory alloy having a first portion and a second portion, a switching leg, first and second electrical contacts, first and second electrical paths and an adaptive control device. The switching leg is coupled to the first and second portions of the shape memory alloy and has first and second positions. The second electrical contact is connected to the switching leg and is electrically isolated from the first electrical contact when the leg is in the first position and is disposed to be electrically connected to the first electrical contact when the leg is in the second position. The first electrical path applies an electrical current through the first shape memory alloy portion and the second electrical path applies an electrical current through the second shape memory alloy portion. The adaptive control device affects movement of the switching leg from the first position to the second position and from the second position to the first position.
U.S. Pat. No. 4,965,545 to Johnson discloses a shape memory alloy rotary actuator. The rotary actuator has a differential pulley pair interconnected by a shape memory alloy wire. The shape memory alloy wire is thermally cycled through its phase change transition temperature and contracts. The tension forces applied by the ends of the wires to opposite sides of the pulley pair result in a net torque which causes relative rotation between the pulley pair and a reference base. A large mechanical advantage of the differential pulley converts a large force working through small distance into a relatively large angular rotation.
It is an object of the present invention to provide a shape memory alloy wire actuator that is simple to manufacture and simple to assemble.
Another object of the invention is to provide a shape memory alloy wire actuator that can be modified to increase or decrease its pulling force by correspondingly increasing or decreasing the number of alloy wire segments forming a serpentine configuration between the body members which move relative to each other.
Accordingly, the shape memory alloy wire actuator of the present invention is hereinafter described. The shape memory alloy wire actuator includes a first body member, a second body member and a strand of shape memory alloy wire. The first body member and the second body member extend along a longitudinal axis and are slidably engageable with one another along that longitudinal axis. The first and second body members move in a linear fashion relative to one another between an extended state and a contracted state. In the extended state, the first and second body members are resiliently biased apart from one another and, in the contracted state, the first and second body members are displaced towards each other. The strand of shape memory alloy wire interconnects the first and second body members in a serpentine manner. As used herein, the term xe2x80x9cserpentinexe2x80x9d describes a sinuous, back-and-forth stranding arrangement of the strand of shape memory alloy wire between the body members. When the shape memory alloy wire is energized or activated, such as by an electrical current, the shape memory alloy wire shortens or contracts causing the first body member and the second body member to move from the extended state to the contracted state. When the shape memory alloy wire is de-energized or deactivated, i.e., the electrical current is removed or shut off, the shape memory alloy wire lengthens causing the first body member and the second body member move from the contracted state to the extended state.
The foregoing and other objects, advantages and features of the invention will become more readily apparent and understood from a consideration of the following detailed description of the exemplary embodiments of the invention when taken together with the accompanying drawings, wherein: